Strange mysql unknown column error - mysql

Question

For some time we have been receiving a "unknown column" error from our mysql server.
The errors look like this:
Unknown column 'JOIN search_table��z[.cc.' in 'field list'
Unknown column '(`IX_cfs$order$make$model`) INNER JOIN search_t' in 'field list'
Unknown column 'eated, cp.stat_sales, cp.stat_views, cp.culture_code' in 'field list'
+ more
The most strange part is that it's completly random which methods in our .NET code that gets the errors. Even methods that does not include any of the reported error tables in the query, sometimes reports the "unkown column" error with SQL code inside that did not belong to that query... :-(
We are running windows 2008, mysql 5.0.45 and the MySQL connector 6.2, .NET 3.5. We have an avarage 250 requests/second with peaks of 750 requests/second. MySQL CPU usage is 10-50% and Memory usage is 5-6 GB (8 GB available).
The errors started only a few months ago, but have become more and more frequent, to the point that we get +500 errors per day from ELMAH. We are suspecting that it could be something with a stressed mysql server, mix-up of connections (either in mysql, or the .NET connection pool).
We have tried to reproduce it locally and on a separate identical server setup, but so far no luck in re-generating the errors, as it does not happen for all sql queries, however a restart of the mysql service eliminates the error for a period of time. But as our userbase and server load is increasing on a 10-15% per month the error have become more an more frequent.
Any help, ideas, advice is very much appreciated...
Additional info:
We are running all external paramters (QueryString, Form post data, webservice parameters, and also internal parameters) thrue a custom function that fixes all SQL injection attempts. And we do not use "dynamic" SQL, only Stored Procedures are used.
On top of this the most frequent method that returns the "unknown column" error is a method in .NET that only takes a int32 as input parameter, an the MySQL SP also only takes a int as parameter.
Also we wrap everything in try-catch-finally, and the error we are getting is from our error handling modules (primarily ELMAH)

Answer 1

It looks like a corrupt query string is getting passed to mySQL.
Your .Net application is almost certainly the culprit.
SUGGESTIONS:
Look again at the code that's making the queries.
If you're lucky, you can easily isolate the actual SQL
Any any case, make sure the relevant code: where you create the query, followed by where you make the query, and finally where you access the result - is wrapped in a try/catch block.
I'm guessing that some unhandled exception might be taking you out of the flow of control path you expect to be taking, resulting in data corruption.